A good mobile telephone cellular communications system should appear to be just like a regular household or business telephone system from the user's perception.
When a user in a car (the "mobile unit") desires to make a call, the mobile telephone unit scans the set-up channels, selects the strongest and locks on for a certain time. Each cell site is assigned a different set-up channel, so locking on to the strongest usually means selecting the nearest cell site in what is termed a "self-location" scheme. Such a scheme does not require the cell sites to locate the mobile unit, but for calls to mobile units, the paging process is longer because no mobile unit location information is available at the cell sites.
A call request sent from the mobile unit is received by a cell site which typically selects a directive antenna for the communications channel. At the same time, the cell site also sends a request for a voice channel to the Mobile Telephone Switching Office (MTSO) via a high-speed data link. The MTSO selects an appropriate voice channel for the call and the cell site links the channel with the directive antenna to the mobile unit. The MTSO also connects the wire-line party through the telephone company central office.
A call from a land-line party to a mobile unit goes first to the telephone company central office which recognizes that the number is for a mobile unit and forwards the call to the MTSO. The MTSO sends a paging message to certain cell sites based on the mobile unit number and a search algorithm. Each cell site transmits the page on its own set-up channel. The mobile unit recognizes its own identification on a strong set-up channel, locks onto it, and responds to the cell site instruction to tune to an assigned voice channel.
Cellular mobile systems in the United States have been designated as Cellular Geographic Service Areas (CGSA). The largest few hundred cities are called Metropolitan Statistical Areas (MSA) and the rest of the CGSAs are called Rural Service Areas (RSA). RSAs are typically adjacent to MSAs, and can also be scattered as remote geographical spots throughout a country.
For further detail regarding mobile communications systems, see Mobile Cellular Telecommunications Systems (McGraw-Hill 1989) by William C.Y. Lee.
An important problem in cellular communications is to provide cost-effective coverage to RSAs that provides adequate service to rural users. Further the RSA system must not interfere with MSA coverage. The cost-effective aspect is crucial in RSAs because of the typically limited number of users.
Accordingly, it is an object of the present invention to provide a new cost-effective mobile communications system.
It is a further object of the present invention to provide a mobile communications system suitable for rural service areas.
It is another object of the present invention to provide a mobile communications system which provides adequate service at minimal complexity, cost, and power.